1. Field Of The Invention
The present invention relates generally to an assembly composed of a hard member and a soft tube fitted onto the hard member for medical applications. More particularly, the present invention relates to an improvement in the assembly of soft tubes and hard members often used as essential components for blood transfusion sets, infusion sets or the like medical devices.
2. Description Of The Prior Art
Many soft tubes each molded of soft synthetic resin, e.g., polyvinyl chloride or the like material have been heretofore used for blood transfusion sets, infusion sets or the like medical devices. Each soft tube is practically used by connecting it to another component, in the form of a hard member, to provide an assembly composed of the hard member and the soft tube for use in a medical device. When such a soft tube, molded of soft polyvinyl chloride or the like material, is connected to the hard member, molded of hard synthetic resin, e.g., polyethylne, polypropylene or the like material, a firm connection is usually carried out by a manual simple fitting operation, because a suitable adhesive employable for the joining of soft and hard synthetic resin is not available at present. In practice, a tight fitting operation is physically performed by dimensioning the inner diameter of the soft tube to be appreciably smaller than the outer diameter of the hard member and forcibly fitting the soft tube onto a fitting portion of the hard member in opposition to a contractive force and a frictional force generated by contraction of the soft tube.
Over time, a slight loosening appears between the soft tube and the hard member. This often leads to trouble in that the soft tube is undesirably disconnected from the fitting portion of the hard member due to reduction of the tightening force which has been induced therebetween.
To solve the foregoing problem, the inventors closely observed disconnection malfunctions as described above. As a result of their observations, they found that disconnections occurred very easily when the close contact region between the soft tube and the hard member disappeared.
FIG. 6 is a side view of a typical conventional assembly composed of a hard member 2 and a soft tube 1 fitted onto a fitting portion 3 of the hard member 2 for medical use. FIG. 7 is a fragmentarily exploded side view of the assembly in FIG. 6. When an intense thrusting force is imparted to the soft tube 1 which has been fitted onto the fitting portion 3 of the hard member 2 under the influence of a reduced magnitude of tightening force, as shown in FIG. 6, the foremost end of the soft tube 1 comes in close contact with the side wall of a flange 4. As a result, the diameter of the foremost end of the soft tube 1 is enlarged with an axial compressive force (see FIG. 7). Consequently, the close contact region between the soft tube 1 and the hard member 2 disappears. If the soft tube 1 is pulled rearwardly to a slight extent while the foregoing state is maintained, disconnection occurs easily with the soft tube 1 because no tightening force exists. In particular, when the conventional assembly is heated during sterilization, the tendency of disconnection of the soft tube 1 becomes remarkably increased.
In view of such malfunctions, it has been proposed that the diameter of the fitting portion 3 of the hard member 2 be dimensioned to become larger towards the flange 4, so as to allow the tightening force to increase correspondingly. Although the tightening force has been increased to some extent with this arrangement a sufficient improvement has not been obtained with this proposal with respect to prevention of undesirable disconnection from occurring with the soft tube 1.
In addition, another proposal has been disclosed in official gazette of Japanese Laid-Open Patent NO. 283651/1988. According to this prior invention, a lower cap for the drip chamber of an infusion set is connected to a soft tube with an improved structure for the purpose of avoiding the problem of undesirable disconnection of the soft tube. However, the improved structure is complicated and therefore the resultant assembly composed of the lower cap and the soft tube is fabricated with many difficulties.
Additionally, it was disclosed that a member made of polyvinyl chloride could be adhered to a member made of polyolefin by using a chlorinated polyolefin-based adhesive. However, once the hard member is coated with this adhesive, it becomes very difficult to insert the hard member into the soft tube because of the increased frictional force. Therefore, this proposal can not be put to practical use.
To substantially improve the conventional assembly composed of a hard member and a soft tube fitted onto the hard member for medical use, the inventors conducted a number of development works and determined that a plurality of projections formed on a flange of the hard member were very effective for preventing the soft tube from being disconnected from the hard member. Further, the inventors found out that particular configurations employed for the soft tube were likewise very effective for the same purpose.